On reading the various entity descriptions, specifically armaments, I find myself wondering what each mean. There are four types of damage that weapons inflict - Physical, Explosive, Ion and Energy.

What does this mean? Are Physical and Explosive synonymous or is Physical focused on a single target and Explosive is splash damage? Can ionic weapons only disable entities and energy weapons only damage shields? Does an Energy damaging weapon become useless once the shields are down and likewise Ionic weapons once the entity is disabled? Are Physical and Explosive useless against shields?

I'm curious also - not even sure if there's a real plan in that regard for some cross-over damage between types (ie if Ion will do any damage to organics, etc).

I imagine that explosive is splash, but also will do higher damage against hulls of vehicles/ships/facilities/stations than energy weapons. Blasters will still have to do *some* damage against everything because they're so ubiquitous.

Physical I could see doing very little damage while shields are up, and a lot more when they're down, both to hull & organics. Mass Drivers come to mind.

Energy I could see doing decent damage to Shields (less than Ion), but more damage without shields to organics than to Hull/armor.

In EAW physical damage would damage ships with shields up. Like the Physical Torpedos would do massive damage ignoring shields and Photon Torps would hit shields doing less with shields up and more with them down. They also had Flack Cannons that did physical damage that would also bypass ships shields but the damage was based on the size of the ship

The damage types are not implemented to have any effect at all and there is no specific information available yet on how (or if) it will be implemented. Likely it's one of those things that will be finalized whenever combat receives some further attention in the future but at the moment it's all rather up in the air.

In response to Kendall, in the Star Wars universe most shield systems were made of combined ray+particle shields.
If you didn't have particle shields then bullets, rocks, missiles, and other ships would be able to crash into you.
If you didn't have ray shields then all of those lasers and ion blasts would cut right through.
Remember the quote about the Thermal Exhaust port?
"It is Ray shielded so you'll have to use Proton Torpedos"
Since it wasn't particle shielded they cut right through.
Likely since it was a thermal exhaust port any ray shield would have reflected the heat back into the station itself so they neglected to use them and settled with just particle shields (one of a few oversights).

So judging by the movies and the Expanded Universe no Proton Torpedos would not "cut through" most normal shields. Which would be why on Hoth the Empire couldn't simply drop torpedos or bombs on the rebel base. Nor could they lay waste with turbolasers from orbit and had to go down to the surface under the shield projection.